Deep hole drill presses or "gun drill presses" as they are sometimes referred, are utilized for boring long and comparatively small diameter holes in metal objects to exacting specifications. A standard gun drill is a replaceable tool comprised, generally, of an elongate shaft having a usually carbide cutting tip situate distally, and an adaptor fixedly mounted by soldering or other means at its proximal end. The adaptor is removably mounted within a chuck assembly of a drill press, the spindle of which revolves at high speeds to accomplish boring action.
While such drills are considered by those skilled in the art to be suitable for their intended purpose, they are not without significant shortcomings. Users of the drill press are required to stock drills of various lengths in order to drill holes of various depths; long shafts for deep holes and shorter shafts for relatively shallow holes. The expense of maintaining the appropriate inventory is considerable and adds to the overall cost of the products of manufacture. Moreover, the adaptor portion of the drill adds to its overall expense as the entire unit must be manufactured or purchased upon exhaustion or breakage of a shaft or tip.
In addition to cost considerations, and as alluded to above, drill presses of the prior art require the repeated interchange of drill tools of differing lengths when boring holes of different depths. Also, when boring a single hole of considerable depth, it is sometimes necessary to begin with a shorter shaft length and progressively interchange drills of greater lengths until the desired depth of the hole is achieved. In either situation, the process becomes tedious and time consuming, involving retraction of the drill from the workpiece, removal of the drill from the chuck assembly and then insertion of a drill having a longer shank back into the press. To further complicate matters, complete removal of the tool is accompanied by unwanted oil spillage because the press operates with pressurized oil behind the adapter.
In the early seventies, efforts were made to resolve the above problems by providing a modified drill of considerable length which could be secured within a novel chuck assembly at different points along the drill's shaft to provide, effectively, different drill lengths from a single drill tool. U.S. Pat. No. 3,701,607 issued to Johnson on Oct. 31, 1972, is one such deep hole drilling tool comprised of three axially aligned, interconnected shanks of different diameter, the last of which being provided with gaskets about its circumference to prevent oil seepage from occurring between the drill and the spindle. This invention was a significant advancement in that it eliminated the requirement of complete retraction and removal of the drill from the collet when shafts of different lengths were called for.
The Johnson invention itself, however, required the manufacture of custom three tier drill tools (and a chuck assembly) which were, in essence, similar in nature to conventional drills with soldered adaptors except that the Johnson tools were capable of slidable adjustability within the spindle's bore and eliminated oil seepage. While the Johnson invention provided important improvements, it did little to control the high costs associated with replacing broken or spent drills, each of which required considerable machining to achieve the appropriate shaft diameter and proper fitting of sealing means.
The subject invention completely obviates all of the shortcomings of the prior art through modification of a standard drill adaptor into a chuck assembly capable of receiving therein various lengths of an elongate shaft. As will be better understood upon review of the summary and detailed description of the invention, below, the subject device provides a means to accomplish deep hole drilling faster and more economically than heretofore possible.